The present invention relates to crankcase ventilation of diesel internal combustion engines, particularly diesel engines used for locomotive applications.
Diesel-powered locomotives generally require an absence of positive crankcase pressure. Yet, during the operation of internal combustion engines, blow-by gas from the combustion chamber during the combustion stroke causes a positive pressure in the crankcase which must be relieved. In the case of locomotive applications, it is desired that the crankcase generally be negatively pressured. Accordingly, since a simple valve or opening in the crankcase is inadequate, a crankcase ventilation system is utilized.
The crankcase ventilation system on a locomotive diesel engine evacuates the excessive crankcase air in the crankcase (from seals and piston blow-by) to the exhaust stream and eventually the atmosphere. Included in the crankcase air is an oil mist that has two negative consequences. First, the oil mist contributes to the engine""s emissions; and second, the oil leaves a coke deposit of carbon that can ignite and start railside fires.
FIG. 1 exemplifies a conventional diesel engine crankcase ventilation system 10, including an oil separator 12 and an evacuator 14. A pipe connection 16 communicates generally horizontally with the crankcase, as, for example, at an upper portion of the oil pan 18. An elbow 20 connects the pipe connection 16 to the oil separator 12, which has an off-set opening 22. Connected to the off-set opening 22 is the evacuator 14. The evacuator 14 has a vertical portion 24 and a horizontal portion 26 demarcated by a bend 28. The end of the horizontal portion 26 is interfaced with an exhaust port 30 which communicates with the engine exhaust system. The bend 28 is fitted with a nozzle assembly 32. The nozzle assembly 32 includes a single orifice nozzle 34 internal to the horizontal portion 26 which is directed down the horizontal portion toward the exhaust port 26, the horizontal portion diameter outwardly tapering with increasing distance from the nozzle assembly. The nozzle assembly 32 is interfaced with a source of pressurized air external to the crankcase, via an air line 36.
In operation, pressurized air emanating from the nozzle blows air toward the exhaust port, causing a low pressure condition in the vertical portion of the evacuator. This low pressure zone communicates with the crankcase through the oil separator to cause crankcase air to be affirmatively evacuated from the crankcase. Oil-laden crankcase air passes through the oil separator, during which the expanded volume and vertical path combine to cause oil to precipitate out of the crankcase air and then flow back into the crankcase.
Several drawbacks of the conventional diesel engine crankcase ventilation system are yet in need of redress, among those being preventing splash oil from entering into the oil separator and improved elimination of oil mist from the crankcase air prior to passing into the exhaust port.
The present invention is an oil separator in the form of a two-stage filtration assembly for a diesel engine crankcase ventilation system which prevents splash oil from entering thereinto beyond a first stage of the oil separator and limits oil mist contamination of crankcase air prior to passing out from a second stage of the oil separator into the exhaust port, thus advantageously improving the engine""s emissions and reducing oil carryover to the exhaust.
The two-stage filtration assembly according to the present invention uses a two-stage approach to crankcase air filtration to effectively separate the oil from the air. The two-stage filtration assembly includes two filters arranged in series, each supported by a sheet metal fabrication housing that is attached to a port in the crankcase, as, for example, at an upper portion of the oil pan.
A first stage filtration assembly includes a first stage filter featuring a wire mesh filtration media contained by a cylindrical tube with perforated (expanded) steel end caps. The first stage filter is mounted horizontally immediately adjacent to the crankcase port. The function of the first stage filter is to remove the large oil particles and any oil splashing adjacent the crankcase. There is a passage associated with the filter which is free of the wire mesh media so as to allow oil to drain from the second stage filter (to be described next) back to the crankcase, thereby the second stage filter to be more effective.
A second stage filtration assembly includes a second stage filter featuring a web filtration media, preferably fiberglass, and is mounted at an acute angle (for example, 20 degrees with respect to horizontal), angling downwardly toward the first stage filtration assembly. The second stage filter is preferably of a hollow cavity cylindrical configuration arranged in the housing such that air from the first stage filter passes through one end into the cavity of the second stage filter, and then passes out through the filter media. The function of the second stage filter is to remove small, airborne oil particles with a high efficiency during the second phase of filtration. Overall advantages of the two-stage filtration system include: removal of oil mist; prevention of railside fires (locomotive applications); and reduction of engine harmful emissions
An evacuator is interfaced with the housing to provide a negative pressure downstream of the second stage filter so as to draw crankcase air from the crankcase to an exhaust port.
In operation, in response to operation of the evacuator, crankcase air flows from the crankcase, through the two-stage filter, through the air evacuation system and then out an exhaust port. The first stage filter serves to keep splashed oil and large oil droplets from migrating to the second stage filter, this oil draining back to the crankcase. At the second stage filter, smaller oil particles that the first stage filter could not eliminate are now filtered out of the crankcase air, wherein oil droplets that form thereat will drain back to the crankcase. The crankcase air that makes it through both the first and second stage filters has had a great amount of oil removed, and flows to the exhaust of the engine in an acceptable composition from its original state. The removed oil is drained back to the crankcase without re-entrainment into the air stream. In this regard, the first stage filter has a low oil removal efficiency which eliminates large oil droplets and oil splashing, while the second stage filter has a high oil removal efficiency which eliminates smaller oil particles suspended in the crankcase air without getting overwhelmed because to the earlier passage of the crankcase air through the first stage filter. The principle of using two different filters, respectively, for two different ranges of oil particle size maximizes the amount of oil that can be withdrawn from the crankcase air of the diesel engine because both types of filters are operating at their respective peak efficiency.
Accordingly, it is an object of the present invention to provide effective oil filtration in connection with a crankcase air ventilation system of a diesel engine.
It is an additional object of the present invention to provide effective oil filtration in connection with a crankcase air ventilation system of a diesel engine, wherein two-stage filtration provides removal of oil droplets progressively over two ranges of oil particle sizes, ranging from a larger size first range to a smaller size second range, so as to thereby provide the advantages of oil mist removal, prevention of railside fires, and reduced harmful emissions.
These and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment.